Pressure control installation for hydraulically shifted automatic transmissions, especially for motor vehicles

ABSTRACT

A pressure control installation for hydraulically shifted automatic transmissions, particularly for motor vehicles, which controls the pressure of a hydraulic medium that effects the shifting operations in dependence on an operating magnitude, whereby the regulation of the pressure is achieved electrically, preferably by the use of a solenoid valve controlling a pilot pressure.

United States Patent Forster et al. 1 1 Apr. 17, 1973 l 4| PRESSURECONTROL INSTALLATION 3,621,864 11/1971 Toncgawa et al. ..251/129 FORHYDRAULICALLY SHHFTED 2,875,634 3 1959 0616111118 et a1 374/868AUTOMATIC TRANSMISSIONS, 3,080,768 3/1963 .Iania ..74/869 3,225,61912/1965 Schaefer... ..74/869 3,324,738 6/1967 Olsen et 74/868 XInventors! Hans-Joachim Fiirster, Stuttgart- 3,398,607 8/1968 Chana..74/868 x Riedenberg; Arwed Von Koch, 3,410,308 11/1968 Moog, Jr. etal.. .251/129 x Stuttgart-Sonnenberg; Hermann 3,461,909 8/1969 Vohringerv ..251/129 X Gaus, Stuttgart-Sillenbuch, all of 3,537,467 1 1/1970Marshall .137/625,64 X Germany FOREIGN PATENTS OR APPLICATIONS [73]Assignee: Daimler-Benz Aktiengesellschaft,

st ff pu t n kh i Germany 740,225 I 1/1955 Great Britain ..137/625.64

[22] Flled: 1970 Primary ExaminerCharles J. Myhre [21 Appl. No.: 25,121Assistant Examiner--Thomas C. Perry AttorneyCraig, Antonelli & Hill [30]Foreign Application Priority Data [57] ABSTRACT Apr. 3, 1969 Germany .Pl9 17 291.9

A pressure control installation for hydraulically shifted 52 US. Cl...74/865, 74/867, 137/625.64, automatic transmissions, Particularly formotor vehi- 251/129 cles, which controls the pressure of a hydraulicmedi- [51] Int. Cl. ..B60k 21/02, F161: 31/02 um h effects h shiftingoperations in dependence [58] Field of Search ..74/865, 866, 867, on anoperating magnitude, whereby the regulation of 74/868, 869; 251/129;l37/625.64 the pressure is achieved electrically, preferably by the useof a solenoid valve controlling a pilot pressure. [56] References CitedUNITED STATES PATENTS 11/1971 Lemieux ..74/869 X 11 Claims, 13 DrawingFigures PATENTE APR 1 7191s SHEET 1 OF 5 I rU I F INVENTORS HANS-JOACHIMFORSTER i .ARWED vow KOCH HERMANN GAUS M lkd ATTORNEYS PATENTEUAPR 11444 3'. 727. 487' SHEET 2 OF 5 34 30 32 3! 33 47 RETURN L a S AINVENTORS =2 5 3 4 'rAANS JOACHIM FORSTER PATH 0F ACCELERATOR LEVERfimfi fi 'h'fg BY 4M ATTORHEYYS PATENTEDAPR 1 Wm 3.727. 487

SHLEI 3 [If 5 FIG. 7

. INVENTgRIgR M M HANS-JOACHIMF d1 d ARWED VON KOCH YHERMANN GAUSATTORNEYS.

PATENTEDAPR1 11918 3'. 727, 487

SHEET 5 0F 5 INVENTORS HANS-JOACHIN FORSTER ARWED VON KOCH HERMANN GAUSATTORNEYS PRESSURE CONTROL INSTALLATION FOR HYDRAULICALLY SHIFTEDAUTOMATIC TRANSMISSIONS, ESPECIALLY FOR MOTOR VEHICLES The presentinvention relates to a pressure control installation for hydraulicallyshifted automatic transmissions, especially for motor vehicles, with aregulation or control of a control pressure effecting either directly orindirectly the shifting operations in dependence on an operatingmagnitude.

Known pressure control installations of this type in which theregulation or control takes place mechanically in dependence on theoperating magnitude, entail the disadvantage that the enlarged adjustingpath for a so-called kick-down position, necessary for the control, wasnot always attainable with certainty by reason of the unavoidabletolerances. Additionally, a mechanical linkage is subjected to wear andrequires frequent readjustment.

It is the aim of the present invention to avoid above all thedisadvantages of the mechanical pressure regulation and to achieve areliable control. Accordingly, the present invention essentiallyconsists in that the regulation or control of the control pressure takesplace in an electrical manner in dependence on the operating magnitude,especially of the accelerator lever position, the engine torque or thevehicle velocity.

Preferably, an electrically actuated valve, especially a magnetic orsolenoid valve is used for that purpose, whose energization iscontrolled by a transmitter controlled by the operating magnitude andwhich is opened against the electrically controlled counter-force by thecontrol pressure to be regulated of the hydraulic medium. An amplifieris preferably interconnected between the transmitter, for example,between a potentiometer or an inductive transmitter actuated by theaccelerator pedal, on the one hand, and the electric control device, forexample, a magnetic or solenoid valve, on the other, which amplifierassures the necessary adjusting force.

The hydraulic pressure which is regulated or controlled electrically,especially by a solenoid valve, can be rendered effective on thedifferent control elements of the automatic transmission shiftingmechanism inthat, in its turn, it controls either directly or indirectlypreferably as pilot or pre-control pressure, a working pressure, forexample, a control or shifting pressure necessary for shifting orengaging the various speeds. The pressure system controlled by thecontrol pressure valve or the magnetic valve may thereby be incommunication with the line system of a hydraulic medium supplied by apump, possibly of modulated pressure, by way of a throttle and may servefor the regulation or control of this pressure, whereby also a controlmay be provided in such a manner that in case of a failure of theelectric control part, the line system of the pressure to be controlledis not rendered inoperable, i.e., put out of action as a result of theinterrupted function of the electric part.

If, as this is customarily the case, the hydraulic pressure in the linesystem of the pressure to be controlled, for example, upstream of aninlet throttle, is variable, then the control pressure valve constructedas magnetic valve has to open farther in case of a large hydraulicpressure than with a small pressure. However, the magnetic force shouldnot change in that case if the pressure to be controlled by the magneticvalve (the pre-control pressure) is to remain constant. By acorresponding shape of the magnet, for example, of a bell-shapedarmature and of an annular gap cooperating therewith in the magnethousing, it may be achieved that the magnetic force remains nearlyconstant within a predetermined stroke range. Preferably, this strokerange is utilized as control range of the magnetic valve.

The magnetic or solenoid valve further permits a versatile additionalapplication since it is utilizable practically in dependence on everyoperating magnitude which might be considered for a control operation.Also, any desired characteristic can be achieved in a relatively simplemanner. Thus, the combined electrichydraulic control system may beutilized, for example, to obtain a shifting-back by means of a full-gasor kick-down signal and to let a range-shifting-back operation proceedas brake shifting operation by means of an idling-gas signal.

Accordingly, it is an object of the present invention to provide apressure control installation for hydraulically shifted automatictransmissions which avoids by simple means the aforementionedshortcomings and drawbacks encountered in the prior art.

Another object of the present invention resides in a pressure controlinstallation for hydraulically shifted automatic transmissions whicheliminates the wear normally occurring in mechanical linkages.

A further object of the present invention resides in a pressure controlinstallation for hydrualically shifted automatic transmissions whichassures reliable control operation and avoids the need for frequentre-adjustments.

Still a further object of the present invention resides in a pressurecontrol installation for hydraulically shifted automatic transmissionsin which the regulation of the control pressure takes place electricallyin dependence on an operating pressure.

These and further objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illustration only, several embodiments in accordance withthe present invention, and wherein:

FIG. 1 is a schematic view of a control installation according to thepresent invention for the operation of an electromagnetic pilot orpre-control valve by means of an accelerator lever;

FIG. 2 is a schematic wiring diagram for the actuation of the magneticvalve in accordance with the present ivention;

FIG. 3 is a cross-sectional view through a magnetic valve in accordancewith the present invention serving as preor pilot control valve;

FIG. 4 is a diagram illustrating the relationship between stroke andattraction or pull force of the magnetic valve;

FIG. 5 is a diagram illustrating the relationship between pressure andadjusting path;

FIG. 6 is a somewhat schematic diagrammatic view of a modifiedembodiment of a control installation with a magnetic valve in accordancewith the present invention actuated in dependence on the engine torque;

FIG. 7 is a diagram illustrating the operation of the controlinstallation of FIG. 6;

FIG. 8 is a somewhat schematic view of a still further modifiedembodiment of a control installation provided with a magnetic valve inaccordance with the present invention, similar to FIG. 6;

FIG. 9 is a diagram illustrating the operation of the controlinstallation of FIG. 8;

FIG. 10 is a somewhat schematic view of still another modifiedembodiment of a control installation with a magnetic valve in accordancewith the present invention operated in dependence on the vehiclevelocity;

FIG. 11 is a diagram illustrating the operation of the installation ofFIG. 10;

FIG. 12 is a somewhat schematic view illustrating a modified embodimentof the control installation of FIG. 10; and

FIG. 13 is a diagram illustrating the operation of the controlinstallation of FIG. 12.

Referring now to the drawing wherein like reference numerals are usedthroughout the various views to designate like parts, and moreparticularly to the schematic view of FIG. 1, reference numeral 20designates in this figure an accelerator lever, such as a gas pedal,actuated by the foot of the driver, which actuates a transmitter 22 bymeans of aplunger 21, that, for example, permits a stroke s of theaccelerator lever 20. The transmitter 22 is constructed, for example, asmulti-partite potentiometer of conventional type having an ohmicresistance variable in dependence on the stroke s, as will be explainedmore fully hereinafter in connection with FIG. 2.

Lines lead from the transmitter 22, for example, by way of switches 23and 24, that permit selective engagement or disengagement of theautomatic shifting mechanism to an amplifier 25 which, for example, bymeans of a transistor, supplies an amplified current in dependence onthe resistance selected by the transmitter 22. The amplified current isfed by way of lines 26 to a magnetic or solenoid valve generallydesignated by reference numeral 27 which is illustrated in detail inFIG. 3 and serves as pilot or pre-control valve for the purpose toregulate in a line 28 a predetermined pilot or pre-control pressure thatis rendered effective on a control slide valve unit generally designatedby reference numeral 29 in a manner to be explained more fullyhereinafter.

A circuit diagram, for example, an electric circuit diagram for theactuation of the magnetic valve 27 is illustrated in FIG. 2. A slidingcontact 22a in the transmitter 22 is slidingly guided by means of theaccelerator lever 20 (not illustrated in FIG. 2) in the direction ofarrow x,x over a line 22b with a resistance R, from a point A by way ofpoints A,, A and A up to point A and controls or regulates thereby thecurrent flowing to the amplifier 25 and thus to the magnetic valve 27.Input resistances R R and R may be arranged in the transmitter 22, andmatching resistances R and R may be arranged in the return line and aprotecting resistance R may be arranged in the input to the transistor25 in the circuit of the magnetic valve 27. Diodes D and D may serve forthe stabilization of the voltage and for the temperature compensation inthe circuit. A change of the pilot or pre-control pressure, for example,as a result of a heating-up of the oil, of the winding or of theamplifier, can be far-reachingly prevented thereby. Also, by a change ofthe matching, i.e., by a change of the resistances such as matchingresistances R and R a parallel displacement of the characteristics ispossible to position the characteristics either higher or lower thanthat shown, for example, in FIG. 5 so that a one-time adjustment inconjunction with the magnetic or pilot control valve 27 may beundertaken.

The transmitter is constructed corresponding to a desired predeterminedcharacteristic in the path-pressure diagram (FIG. 5) so that whendepressing the accelerator lever, each position of the lattercorresponds maximum value depending on the position of the acceleratorlever 20.

As is illustrated in FIG. 3, the solenoid valve generally designated byreference numeral 27 includes a multi-partite housing 30 in which isaccommodated the magnetic winding or coil 31 supplied with current byway of the line 26. An annular gap 34 is formed between a housing crosswall 32 laterally delimiting the magnetic winding 31 and a sleeve-shapedpart 33, acting as magnetic core, of the valve housing 30; thebellshaped armature 35 is thereby adapted to approach more or less theannular gap 34 by means of its rim 36 and/or is able to enter more orless into the annular gap 34.

A valve needle 39 is rigidly connected with the armature 35, adjustablein the longitudinal direction by means of a threaded portion 37 and nut38; the valve needle 39 is slidingly supported appropriately in thebearing 40 of frictionless, synthetic resinous material, for example, ofTeflon, and is suspended at a leafspring 41 secured at the housing bymeans of screw 41a. The bearing support may also be realized by means oftwo such bearings 40 and without leaf-spring 41. The leaf spring 41 isclamped fast by means of the screw 41a and extends past the screw 35a upto the threaded portion 37 which is carried by the leaf spring 41. Tothat end, the leaf spring 41 may, for example, engage in a thread of thethreaded portion 37 so that the valve 42 is lifted off from its seat 43by the spring force of the leaf spring 41. The valve needle 39cooperates by means of its conical needle end 42 with a seat 43 in thevalve housing 30 and thereby controls an opening 44 for the flowtherethrough of the hydraulic medium. The space 45 upstream of the valveneedle 39, 42, forms a part of the feed line 28 whereas the space 46downstream of the valve needle 39 is connected with a return line 47leading to a supply tank or the like (not shown).

The line 28 and therewith the space 45 which is under a pilot orpre-control pressure p is in communication by way of a throttle 48 witha feed line 49, to which is supplied a hydraulic medium at apredetermined pressure from a pump 49a by way of suitable conventionalcontrol devices 49b (FIG. 1).

The control slide valve unit 29 (FIG. 1) for the control or regulationof the control pressure serving for the direct or indirect shifting of atransmission shifting element, for example, of a command slide valvemember, is provided with a piston-like slide valve portion 50 and with apiston-like slide valve portion 51. The slide valve portion 50 is underthe effect of a compression spring 52 which is supported with its oneend (right end as viewed in FIG. 1) at the slide valve member 50 andwith its other end (left end as viewed in FIG. I) by means of a springwasher 53 at a fixed abutment 54 in the slide valve housing 55. Theslide valve part 51, in its turn, is under the effect of a compressionspring 56 which seeks to press the slide valve part 51 toward the leftas viewed in FIG. 1 against a cover 57 of the housing 55 and, on theother, supports itself against a spring guide part 58. The latter isthereby acted upon on the side opposite the spring 56, by a spring 59which is supported with its opposite end against the spring washer 53that is secured on a guide pin 60 supported unilaterally at an abutment58a of the spring guide part 58. The springs 52, S6 and 59 are sodimensioned that the strength of the spring 59 exceeds that of thespring 52 and the strength of the spring 52 exceeds that of the spring56.

The space 61 at the left end of the slide valve part 51 is connectedwith the line 28 for the pilot or pre-control pressure, for example, byway of a line 28a whereas a control groove 62 at the slide valve part 50is connected, for example, by way of a branch line 490 with the line 49that is under the modulating pressure p,,.. With a small movement of theslide valve part 50 toward the right as viewed in FIG. 1, the controlgroove 62 may enter into communication with a further control groove 63to which is connected a line 64 that leads to the shifting elements, forexample, to the command slide valves of the automatic transmission andis connected by means ofa branch line 640 with the space 65 at the rightend of the slide valve part 50.

Further lines may be valved by the control slide valve 29 as can bereadily seen from FIG. 1. Thus, for example, a control groove 66 isconnected with a line 67 which actuates an idling-gas" signal when thecontrol groove 66 is opened up by the slide valve part 51 and thus isconnected with a discharge, for example, at 68. A further control groove69 is in communication with a line 70 in order to produce a kick-downsignal when the control groove 69, upon depressing fully the acceleratorlever 20 and 'thus displacing the slide valve part 51 toward the right,is connected by a cross bore 71 in the slide valve part 51 with theinterior thereof and therewith with the exhaust or discharge line 68.

OPERATION The operation of the installation described so far is asfollows:

As long as the acclerator lever 20 is not depressed and the winding 31of the magnetic valve 27 is de-energized, i.e., without current(corresponding to point A in FIGS. 2 and 5) due to the blocking actionof the transistor 25 which is non-conductive when its base voltage is atthe same potential as its emitter voltage, the valve needle 39 is liftedoff from its seat 43 by the hydraulic medium so that the medium flowingthrough the line 28 is able to flow off, without resistance, by

way of exhaust 47 and therewith no pressure is able to build up in theline 28.

A diagram is illustrated in FIG. 4 in which the attraction or pullingforce P, with which the armature 35 is attracted by the magnet whencurrent is supplied to the winding 31, and with which the valve needle39 is thus pressed against its seat 43, is plotted in dependence on thestroke h of the valve needle 39. By an appropriate, corresponding designand shape of the annular gap 34 and of the armature 35, it can beachieved that an attracting force P can be realized thereby with thecharacteristics illustrated in the diagram of FIG. 4. If this stroke his selected in such a manner that the valve needle 39 is located in theclosing position at the point I1 and at the point h in the maximumopening position, then within this operating range a, the force P, i.e.,the energizing current I for the winding 31, and in dependence thereonthe pilot or pre-control pressure p,. in the line 28 remains practicallyconstant notwithstanding the fact that the flow cross-section betweenthe valve needle end 42 and the valve seat 43 increases -with the valvestroke. In other words, FIG. 4 illustrates the attraction force-pathdiagram of the solenoid valve whereby the attraction force P of themagnet is plotted against the stroke, and more particularly beyond theclosing position h of the valve, i.e., under the assumption that a valveseat would not be present. From the characteristic curve P resultingtherefrom, that range is selected for the effective stroke a in whichthe attraction force P and correspondingly also the precontrol Ipressure in the line 28 is constant.

The pilot or pre-control pressure p, in the line 28 as well as thecontrol pressure p, in the line 64 which is used forthe shiftingoperations is plotted in the diagram of FIG. 5 against the path s of theaccelerator lever 20. By reason of the throttle 48 a certain pressurebuilds up upstream of the throttle 48 in the line 49, which pressurecontinues with a corresponding adjustment of the slide valve part 50 inthe line 64 and produces therein a predetermined working pressure(control or shifting pressure) p, which corresponds with a non-actuatedaccelerator lever 20, for example, in the diagram according to FIG. 5 tothe point B If the accelerator lever 20 is depressed so that the slidingcontact or potentiometer arm 22a moves in a direction opposite thedirection x,, i.e., in the direction of arrow x from point A to point Aand the solenoid winding 31 is therefore supplied with current, then thevalve needle 39 is forced with increasing current strength against thevalve seat 43 whereby a pilot or pre-control pressure is able tobuild-up in the line 28. This pilot or pre-control pressure p,. which issubstantially constant as the sliding contact or potentiometer arm 22amoves from point A, to point A acts in the space 61 on the slide valvepart 51 which thereby'displaces the slide valve part 51 toward the rightas viewed in FIG. 1 while compressing the realtively weak spring 56. Thecontrol groove 66 is thereby covered or closed off by the right edge ofthe slide valve part 51 so that the idling-gas" signal is renderedineffective. After a predetermined stroke of the slide valve part 51,the latter abuts against the left end of the spring guide part 58.During this stroke s up to the point A in FIGS. 2 and 5, a furtherincrease of the pilot or pre-control pressure p,, as well as also of thecontrol pressure p, in the line 64 does practically not occur.

During the further actuation of the accelerator lever 20, during whichthe sliding contact or potentiometer arm 22a moves from point A alongthe resistor R, in the direction of arrow x for example, with gradualdecrease of the interconnected resistance R, (FIG. 3) and amplificationof the energizing current of the solenoid winding 31, the right spring52 is now also compressed by means of the center spring 59 whichinitially still remains non-yielding or inflexible, in that the springplate 53 lifts off from its abutment 54. The control part 50 therebyretains in principle its position whereby the pilot or pre-controlpressure p in the space 61 and the control pressure p, in the line 64and in the space 65 increases approximately proportionally correspondingto the stroke s;, in FIG. 5 from point A, to point A and from point B topoint B respectively, i.e., proportionally to the resistance decrease atthe point where the potentiometer arm 22a contacts the resistor R,. Thepressure p, in the space 65 thereby acts in opposition to the pressurep, in the space 61. The pressure p, controlled by the piston 50 in line64 reaches at the point B, the value of the feed or supply pressure inline 490. During a further increase of the pressure p from point A topoint A, the piston 50 is forced toward the right against the housing bythe piston 51, the spring guide means 58, the compression spring 59, andthe pressure pin 60 so that the line 64 comes into free communicationwith the line 49, and therewith the control pressure p, assumes in thelast stroke portion 5 the maximum pressure corresponding to themodulating pressure p, in the line 49.

The feed or modulating pressure p,,, is appropriately adjustable byconventional means whereby also the maximum value of the controlpressure p, is adjustable at the point B, via the resistance R The pilotor pre-control pressure p, attains the socalled full-gas point at pointA, A;,. With a completely depressed accelerator lever 20, i.e., after apedal stroke s.,, the pilot or precontrol pressure p,, with acorresponding construction of the transmitter 22 also increases to thevalue of the supply or inlet pressure p, which is reached, for example,at point A At point A the end position of the accelerator lever isreached.

As precontrol pressure the idling pressure p,. upstream of the solenoidvalve 27 is lower as a rule than the supply pressure produced at thepump 49a. Since the oil losses depend from the pressure, they arecorrespondingly small. The switches 23 and 24 have the purpose to engagecertain speed ranges of the transmission, i.e., for example, only thesecond speed which in many cases is particularly advantageous.

It is assumed in the embodiment according to FIG. 6 that the magnetwinding 31 of the magnetic pilot control valve 27 is supplied with acurrent proportional to the torque of the engine by way of the line 26.Different correcting magnitudes, such as rotational speed andtemperature may be again taken into consideration. The magnetic valveregulates or controls therewith a pilot or pre-control pressure p of thehydraulic medium flowing through the line 28, proportional to the torquewhich hydraulic medium is supplied from a pump 149a by way of the line149 and the throttle 48.

This pressure p is again fed to the end face of a slide valve part 151in the space 161 of a slide valve unit generally designated by referencenumeral 129 for the control of a working pressure in dependence on thetorquewhereby the slide valve part 151 is force- 7 lockingly supportedagainst the slide valve part 150 by a spring 152 and after a certainrelative stroke of the piston part 150 is positively supported by apressure pin 160. Y

A load or receiver line 72a, 72b with an interconnected control device72c of any conventional .construction, for example, for a clutch or aservo mechanism of the automatic shifting system, branches off from theline 149 whereby the line 72b terminates in the space 165 on the rightside of the control slide valve part 150 whereas a line 149:: leads tothe groove 162 of the control part 150 of the control slide valve unit129. A lubricating circulatory system 73 connected to the pump 149a mayalso be controlled by the control slide valve 129. The arrangement isthereby made in such a manner that upon movement of the control slidevalve part 150 toward the left, the control edge 73a opens thelubricating circulatory system 73 before a control edge 74a opens up areturn line 74.

In the diagram according to FIG. 7, the working pressure p,, in the line149 is schematically plotted against the torque M Up to a torque M,,,the slide valve part 151 is displaced against the effect of the spring152 by the pilot or pre-control pressure p,. effective in the space 161.Since the spring pressure is practically constant in that case, also theworking pressure p remains practically constant. However, as soon as theslide valve parts 151 and 150 abut against one another, the pressures inthe spaces 162 and 165 operating against the pilot or pre-controlpressure p,. increase proportionally to the pilot control pressure p,corresponding to the curve p in FIG. 7.

In contradistinction to the shifting arrangement according to FIG. 6,described hereinabove, it may be achieved with a shifting arrangementaccording to FIG. 8 that the pilot or pre-control pressure p,, in theline 28 controlled by the magnetic pilot control valve 27 initiallyinfluences the modulating pressure p,,,, and the latter only influencesthe working pressure p,,. Such a shifting arrangement has the advantagethat in case of failure of the electric transmission, a collapse of theworking pressure p,, is avoided. However, it is necessary in connectionwith the construction according to FIG. 8 that the current fed to themagnetic pilot control valve be inversely proportional to the torque.

A control slide valve 80 (FIG. 8) which serves for the control of themodulating pressure p,,,, is constructed as differential slide valvemember and is provided with an end surface F, in the pressure space 81and with an annular surface F at a control spool-portion 82 offset to a7 larger diameter with respect to the remaining slide valve body. Thespace 81 in front of the end surface F, is connected by way of alongitudinal bore 84a and a cross bore 84b, which is constructed asthrottle, with the annular space 85 in front of the annular surface FThe pilot or pre-control pressure p,, acting against the end surface F,and the controlled modulating pressure p acting on the annular surface Fthereby operate against the compression spring 83.

The annular space 85 is connected by way of a line 128 with the space161 in front of the slide valve part 151 of the control slide valve unit129 which, as to the rest, is constructed in the same manner as in thecase of FIG. 6, whereby exclusively the shifting arrangement of thecontrol slide valve unit 129 is changed to the extent that the line 149together with the line 72 leading to the receiver or load places is notconnected directly with the line 28 for the pilot or pre-controlpressure p,. by way of a throttle. The line 149, instead, leads to thespace 86 at the modulating pressure control slide valve 80, from wherethe pressure can continue by way of a control edge 86a of the controlslide valve 80 into the annular space 85 and is controlled therebycorresponding to the position'of the control slide valve 80.

With an increasing torque, the pilot or pre-control valve 27 regulates adecreasing pressure p,., as can be seen from the diagram of FIG. 9, inwhich the pressure p is plotted against the torque M in the curveindicated in dash and dotted line. With the decrease of the pressure palso the hydraulic pressure acting against the end surface F of themodulating pressure control slide valve 80 decreases so that the spring83 seeks to displace the control slide valve 80 toward the left. As aresult of the decreasing throttle effect at the control edge 86a, thepressure at the annular surface F increases until the equilibrium isre-established with respect to the spring 83. The modulating pressure pand therewith also the working pressure p,, increases approximatelycorresponding to the engine torque M, according to the curves indicatedin FIG. 8.

If the magnetic valve 27 fails for any reason, then the pressure p,. atthe end surface F, collapses. The slide valve 80 is displaced toward theleft and closes the line 28 with respect to the bore 84a and therewithwith respect to the line 128 and 149. A high pressure corresponding tothe maximum modulating pressure 12,, results in that case at the annularsurface F in a manner similar as described before so that thetransmission cannot fail by reason of inadequate oil pressure.

A shifting arrangement for the change of a pilot or pre-control pressurep, in dependence on the driving velocity of the vehicle or on arotational speed of the vehicle drive is schematically illustrated inFIG. 10.

A rotational speed transmitter 222 of conventional construction, forexample, as shown in FIG. 2 in connection with transmitter 22, utilizinga potentiometer whose potentiometer arm is displaced as a function ofthe rotational speed, for example, by a centrifugal governor, not shownin detail since of conventional construction, regulates a current whichis supplied by way of an amplifier 225 to the solenoid valve 27operating as pilot or pre-control valve whereby the current energizingthe magnet coil is a function of the velocity or rotational speed. Theline 28 which is connected by way ofa throttle 48 with a line 249 fed bya pump 249a, also continues to a space 281 which acts on the controlslide valve 280 on one end surface thereof and seeks to displace thesame toward the left against the effect of a spring 283 accommodated ina space 285. A line 266 branched off from the line 249 and having thepressure p,, which is controlled by the control slide valve 280 at acontrol edge 266a, may lead to the shifting elements of thetransmission, for example, to the rotationalspeed-dependent side of thecommand slide valves whose opposite sides are acted upon, for example,dependent on the torque. A branch line 266b leads by way of a throttleto the space 285 so that the pressure of the medium present in the space285 and the pressure of the spring 283 act in opposition to theelectrically controlled pressure p, in the space 281. Further workingstations can be connected to the line 249.

A diagram is illustrated in FIG. 11 in which the pressure p is plottedagainst the velocity v and from which follows that the pressure p in theline 266 as also the pilot or pre-control pressure p,, in the line 28increases proportionally with the rotational speed or velocity v.

The embodiment according to FIG. 12 differs from that of FIG. 10 only inthat the control slide valve 280 is constructed as differential slidevalve having the piston parts 282a and 28212, whereby thecharacteristics for the hydraulic pressures p, and p illustrated in FIG.13 can be attained. The slide valve 280 is made in one piece but mayalso be composed of two piston parts without affecting its operation.

In the embodiments according to FIGS. 10 to 13, the pressure p,, is thusincreased either additively (FIG. 13) or proportionally (FIG. 11) by wayof the hydraulic control slide valve. If the lands or piston parts 282aand 28212 are of identical dimensions (FIG. 10) then also the pressuresp,, and p are equal-apart from the spring pressure of the lands orspring 283. If the lands or piston parts 282a and 282b are of unequaldiameters (FIG. 12), then p,, is larger than p in order that the controldevice is in equilibrium which is desirable.

While we have shown and described several embodimentsin accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not which to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

We claim:

1. A pressure control installation for hydraulically shifted automatictransmission of a machine having a line system for a pressure fluidcomprising a source of pressure fluid for the line system, transmittermeans for generating an electric output signal in dependence on anoperating magnitude of the machine, control means connected in the linesystem for providing a control pressure for shifting of thetransmission, said control means including electric pressure regulatingmeans responsive to the electric output signal of said generating meansfor effecting the regulation of the control pressure in dependence onthe operating magnitude, said electric pressure regulating meansincluding solenoid valve means having an electro-magnet and including amagnetic housing and magnetic core with an annularly shaped gaptherebetween, and a bell-shaped armature arranged for movement of itscylindrical rim within said annularly shaped gap such that the range ofmovement of said armature is effected under an essentially constantmagnetic force produced by said electromagnet and said electric outputsignal, said control means including a further pressure regulatingmeans, said electric pressure regulating means applying a pilot controlpressure to said further pressure regulating means, and at least oneworking pressure supplied by said pressure source being applied to saidfurther pressure regulating means in opposition to the pilot controlpressure, said further pressure regulating means being responsive to theapplied pressures for regulating the control pressure for effecting theshifting of the transmission, said further pressure regulating meansactuated by the electrically controlled pilot control pres sureincluding a first slide valve means acted upon by said control pressureand a second slide valve means which is acted upon by a working pressuresupplied by said pressure source and controlled by said further pressureregulating means in a direction opposite to .said pilot controlpressure, a spring guide means having a pressure element displaceablerelative thereto in one direction and provided with spring abutmentmeans as well as three spring means interconnected between said firstand second slide valve means, the weakest one of said spring means beingarranged between the first slide valve means and the spring guide means,the second strongest spring means being arranged with prestress betweenan abutment at the spring guide means and the spring abutment meanswhereas the third spring means having a strength intermediate the firstand second spring means is supported, on the one hand, at the secondslide valve means and, on the other, at the spring abutment meansforcing the same against a fixed abutment.

2. A pressure control installation according to claim 1, wherein saidfurther pressure regulating means includes means responsive to theelectrically controlled pilot control pressure for producing signals forat least one of two output pressures consisting of an idling pressuresignal and a full-load pressure signal.

3. A pressure control installation according to claim 1, characterizedin that the machine is a motor vehicle and the operating magnitude isthe position of an accelerator lever.

4. A pressure control installation according to claim 1, characterizedin that said magnetic valve means is opened by a pilot control pressureof said hydraulic medium.

5. A pressure control installation according to claim 1, characterizedin that an amplifier means is connected between thetransmitter means andthe electric pressure regulating means.

6. A pressure control installation according to claim 5, characterizedin that said transmitter means is a potentiometer.

7. A pressure control installation according to claim 1, characterizedby means for supporting the armature for substantially frictionlessmovement.

8. A pressure control installation according to claim 7, wherein saidsupporting means is a leaf spring. I

9. A pressure control installation for hydraulically shifted automatictransmission of a machine having a line system for a pressure fluidcomprising a source of pressure fluid for the line system, transmittermeans for generating an electric output signal in dependence on anoperating magnitude of the machine, control means connected in the linesystem for providing'a control pressure for shifting of thetransmission, said control means including electric pressure regulatingmeans responsive to the electric output signal of said generating meansfor-effecting the regulation of the control pressure in dependence onthe operating magnitude, said electric pressure regulating meansincluding solenoid valve means having an electromagnet and including amagnetic housing and magnetic core with an annularly shaped gaptherebetween, and a bell-shaped armature arranged for movement of itscylindrical rim within said annularly shaped gap such that the range ofmovement of said armature is effected under an essentially constantmagnetic force produced by said electromagnet and said electric outputsignal, said control means include a further pressure regulating means,said electric pressure regulating means applying a pilot controlpressure to said further pressure regulating means, and at least oneworking pressure supplied by said pressure source being applied to saidfurther pressure regulating means in opposition to the pilot controlpressure, said further pressure regulating means being responsive to theapplied pressures for regulating the control pressure for effecting theshifting of the transmission, said further pressure regulating meansincluding first means responsive to a predetermined pilot controlpressure applied thereto for providing a constant output controlpressure from said further pressure regulating means, and second meansresponsive to a pilot control pressure exceeding the predeterminedpressure for providing an output control pressure which increases inaccordance with increasing pilot control pressure within a predeterminedrange until a maximum pilot control pressure is obtained whereby amaximum constant output control pressure is provided, said -first meansincluding a first slide valve and a first spring means biasing the slidevalve in a direction opposite to the pilot control pressure, such thatthe first slide valve abuts against a spring guide means in response tothe predetermined pilot control pressure, and said second meansincluding a second slide valve and a second spring means arrangedbetween the second slide valve and said first means, said second springmeans being compressed in response to the pilot control pressureexceeding the predetermined pressure and causing the second slide valveto move against a fixed abutment.

10. A pressure control installation for controlling pressure fluid in aline system comprising a source of pressure fluid for the line system,control means connected in the line system for regulating the pressuretherein including electric pressure regulating means providing a pilotcontrol pressure and further pressure regulating means for providing anoutput control pressure, said further pressure regulating means beingactuated by the electrically controlled pilot control pres sure andincluding a first slide valve means acted upon by said pilot controlpressure and a second slide valve means which is acted uponby a workingpressure supplied by said pressure source and controlled by said furtherpressure regulating means in a direction opposite to said pilot controlpressure, a spring guide means having a pressure element displaceablerelative thereto in one direction and provided with spring abutmentmeans as well as three spring means interconnected between said firstand second slide valve means, the weakest one of said spring means beingarranged between-the first slide valve means and the spring guide means,the second strongest spring means being arranged with prestress betweenan abutment at the spring guide means and the spring abutment meanswhereas the third spring means having a strength inter mediate the firstand second spring means is supported, on the one hand, at the secondslide valve means and, on the other, at the spring abutment meansforcing the same against a fixed abutment.

1. A pressure control installation for hydraulically shifted automatictransmission of a machine having a line system for a pressure fluidcomprising a source of pressure fluid for the line system, transmittermeans for generating an electric output signal in dependence on anoperating magnitude of the machine, control means connected in the linesystem for providing a control pressure for shifting of thetransmission, said control means including electric pressure regulatingmeans responsive to the electric output signal of said generating meansfor effecting the regulation of the control pressure in dependence onthe operatiNg magnitude, said electric pressure regulating meansincluding solenoid valve means having an electro-magnet and including amagnetic housing and magnetic core with an annularly shaped gaptherebetween, and a bell-shaped armature arranged for movement of itscylindrical rim within said annularly shaped gap such that the range ofmovement of said armature is effected under an essentially constantmagnetic force produced by said electromagnet and said electric outputsignal, said control means including a further pressure regulatingmeans, said electric pressure regulating means applying a pilot controlpressure to said further pressure regulating means, and at least oneworking pressure supplied by said pressure source being applied to saidfurther pressure regulating means in opposition to the pilot controlpressure, said further pressure regulating means being responsive to theapplied pressures for regulating the control pressure for effecting theshifting of the transmission, said further pressure regulating meansactuated by the electrically controlled pilot control pressure includinga first slide valve means acted upon by said control pressure and asecond slide valve means which is acted upon by a working pressuresupplied by said pressure source and controlled by said further pressureregulating means in a direction opposite to said pilot control pressure,a spring guide means having a pressure element displaceable relativethereto in one direction and provided with spring abutment means as wellas three spring means interconnected between said first and second slidevalve means, the weakest one of said spring means being arranged betweenthe first slide valve means and the spring guide means, the secondstrongest spring means being arranged with prestress between an abutmentat the spring guide means and the spring abutment means whereas thethird spring means having a strength intermediate the first and secondspring means is supported, on the one hand, at the second slide valvemeans and, on the other, at the spring abutment means forcing the sameagainst a fixed abutment.
 2. A pressure control installation accordingto claim 1, wherein said further pressure regulating means includesmeans responsive to the electrically controlled pilot control pressurefor producing signals for at least one of two output pressuresconsisting of an idling pressure signal and a full-load pressure signal.3. A pressure control installation according to claim 1, characterizedin that the machine is a motor vehicle and the operating magnitude isthe position of an accelerator lever.
 4. A pressure control installationaccording to claim 1, characterized in that said magnetic valve means isopened by a pilot control pressure of said hydraulic medium.
 5. Apressure control installation according to claim 1, characterized inthat an amplifier means is connected between the transmitter means andthe electric pressure regulating means.
 6. A pressure controlinstallation according to claim 5, characterized in that saidtransmitter means is a potentiometer.
 7. A pressure control installationaccording to claim 1, characterized by means for supporting the armaturefor substantially frictionless movement.
 8. A pressure controlinstallation according to claim 7, wherein said supporting means is aleaf spring.
 9. A pressure control installation for hydraulicallyshifted automatic transmission of a machine having a line system for apressure fluid comprising a source of pressure fluid for the linesystem, transmitter means for generating an electric output signal independence on an operating magnitude of the machine, control meansconnected in the line system for providing a control pressure forshifting of the transmission, said control means including electricpressure regulating means responsive to the electric output signal ofsaid generating means for effecting the regulation of the controlpressure in dependence on the operating magnitude, said electricpressure regUlating means including solenoid valve means having anelectromagnet and including a magnetic housing and magnetic core with anannularly shaped gap therebetween, and a bell-shaped armature arrangedfor movement of its cylindrical rim within said annularly shaped gapsuch that the range of movement of said armature is effected under anessentially constant magnetic force produced by said electromagnet andsaid electric output signal, said control means include a furtherpressure regulating means, said electric pressure regulating meansapplying a pilot control pressure to said further pressure regulatingmeans, and at least one working pressure supplied by said pressuresource being applied to said further pressure regulating means inopposition to the pilot control pressure, said further pressureregulating means being responsive to the applied pressures forregulating the control pressure for effecting the shifting of thetransmission, said further pressure regulating means including firstmeans responsive to a predetermined pilot control pressure appliedthereto for providing a constant output control pressure from saidfurther pressure regulating means, and second means responsive to apilot control pressure exceeding the predetermined pressure forproviding an output control pressure which increases in accordance withincreasing pilot control pressure within a predetermined range until amaximum pilot control pressure is obtained whereby a maximum constantoutput control pressure is provided, said first means including a firstslide valve and a first spring means biasing the slide valve in adirection opposite to the pilot control pressure, such that the firstslide valve abuts against a spring guide means in response to thepredetermined pilot control pressure, and said second means including asecond slide valve and a second spring means arranged between the secondslide valve and said first means, said second spring means beingcompressed in response to the pilot control pressure exceeding thepredetermined pressure and causing the second slide valve to moveagainst a fixed abutment.
 10. A pressure control installation forcontrolling pressure fluid in a line system comprising a source ofpressure fluid for the line system, control means connected in the linesystem for regulating the pressure therein including electric pressureregulating means providing a pilot control pressure and further pressureregulating means for providing an output control pressure, said furtherpressure regulating means being actuated by the electrically controlledpilot control pressure and including a first slide valve means actedupon by said pilot control pressure and a second slide valve means whichis acted upon by a working pressure supplied by said pressure source andcontrolled by said further pressure regulating means in a directionopposite to said pilot control pressure, a spring guide means having apressure element displaceable relative thereto in one direction andprovided with spring abutment means as well as three spring meansinterconnected between said first and second slide valve means, theweakest one of said spring means being arranged between the first slidevalve means and the spring guide means, the second strongest springmeans being arranged with prestress between an abutment at the springguide means and the spring abutment means whereas the third spring meanshaving a strength intermediate the first and second spring means issupported, on the one hand, at the second slide valve means and, on theother, at the spring abutment means forcing the same against a fixedabutment.
 11. A pressure control installation according to claim 10,wherein the line system connected to the pressure source includes afirst line system for the electrically controlled pilot control pressureacting on the further pressure regulating means which is operativelyconnected with a second line system for the working pressure supplied bythe pressure source by way of a throttle means.